Abstract

The Precambrian record on both sides of the British-Scandinavian Caledonides begins in late Archean times with a c.3.0-2.6 b.y. old crust-forming episode, the Presvecokarelian episode of eastern U.S.S.R. and northern Finland and the Scourian episode of northwestern Britain, with rocks of corresponding age in northwestern Norway. As yet there is no unambiguous isotopic evidence of the existence of products of early Archean times, such as found in Greenland.

Products of an episode of earth history in early Proterozoic times (2.5-2.4 or ?2.2 b.y.) in which igneous activity and tectonism in localized elongate zones dominated, at crustal levels now exposed, are present in northwestern Britain (Inverian episode), and Soviet Karelia. The initial stages of the subsequent Svecokarelian episode (Laxfordian episode in northwestern Britain) is represented by c.2.2-2.0 b.y. sedimentary and volcanogenic sequences which are markedly different in the Karelian and Svecofennian parts of the Svecokarelides. A continent-continent collision model, with subduction of intervening oceanic crust, satisfies the known constraints for the evolution of this orogen. The tectonothermal and igneous activity occurred mainly c. 1.9-1.7 b.y. ago. Post-orogenic volcanism and emplacement of rapakivi granites followed over a period of c.300 m.y. and there was other sedimentary, igneous and metamorphic activity, possibly in two main episodes, before the initiation of the c.1.2-0.9 b.y. Sveconorwegian orogeny.

The products of the c.1.2-0.9 b.y. tectonothermal and igneous episode predominate in southern and southeastern and southwestern Sweden and are represented in tectonic units of the basement in the Caledonides of Norway. The orogen is considered to be a continuation of the Grenville orogen of western Canada whose products are also present in Rockall and in basement rocks in the Caledonides of northwestern Britain. Coeval with an early part of this middle-late Proterozoic episode was the formation of c.1.2 b.y. old Jotnian sandstones and dolerites while paleomagnetic evidence from 1.0-0.9 b.y. old dolerites in Sweden indicates juxtaposition of northwestern Europe and North America at this time.